About ES6 syntax 1 (let and const)

This article introduced ES6 syntax (let and const)

This post is to summarize ES6 syntax, which I recently revisited in preparation for a coding test.

ES6 stands for ECMAScript, which was released in 2015, and is a standardized version of JavaScript.

About variable declarations (let, const)

These are the keywords used to declare block-scoped variables.

• let: No duplicate declarations are allowed, so it cannot be declared multiple times with the same name. The value can be reassigned after the variable is declared.
• const: The declared variable is a constant, so the value cannot be changed once assigned.

Example of a let declaration

let count = 0;
count = 5; // can be reassigned

if (true) {
  let count = 10; // Declare a new block scope variable
  console.log(count); // output: 10
}

console.log(count); // output: 5 (variables outside the block are not affected)

Example of a const declaration

const PI = 3.14159;
PI = 3.14; // Error - constants cannot be reassigned

if (true) {
  const age = 30; // Declare a new block scope constant
  console.log(age); // output: 30
}

console.log(age); // Error - constant cannot be accessed from outside the block

What is a block-scoped variable?

A variable that is valid only within the block in which it is declared.